An electric power tool, such as an electric screwdriver or an impact wrench, uses a battery pack (rechargeable battery) as a power source. This eliminates the need for an electric cord connected to an external power supply such as a commercial power supply. Further, the electric power tool may be used where there is no external power supply. Japanese Laid-Open Patent Publication No. 2014-54703 describes an example of an electric power tool.
The electric power tool includes a control unit provided with an undercut function that stops performing discharging when the battery voltage is low (e.g., 2.0 V/cell). However, when the temperature of the battery pack is low (e.g., 5° C. or lower), the discharge of a large amount of current would cause a large voltage drop. In such a case, if the electric power tool is used under a situation in which the load is large and the temperature is low, activation of a trigger switch would also cause the undercut function to become effective and stop the operation of the electric power tool. As a result, it is difficult for the user to acknowledge whether the electric power tool stopped operating due to the depletion of the battery capacity (undercut function) or due to a voltage drop in a low-temperature condition.